Sub-frame intrusion control by ramping during frontal impact for electric vehicle battery protection

ABSTRACT

A frame structure is adapted to absorb energy from frontal impacts and extends under a front portion of the body frame. The frame structure includes a rear sub-frame located below and in front of a pair of side frame under-members, and at least one ramp connected to the pair of side frame under-members for directing rearward sliding movement of the rear sub-frame and attached structures downwardly beneath a battery assembly. A catching surface engages a steering gear to improve energy absorption during frontal impacts. A reinforcement bracket attached to the pair of side frame under-members defines a pocket for temporarily catching the rear sub-frame providing an energy absorption path before releasing the rear sub-frame to slide past. A tether is connected between the pair of side frame under-members and the rear sub-frame for holding the rear sub-frame against the ramp to increase energy absorption.

FIELD OF THE INVENTION

The invention relates to a land vehicle having supporting wheels toengage a surface over which the vehicle moves, a motor or hybridelectric engine enabling the vehicle to be moved along the surface, aframe providing support for a vehicle body, where at least a portion ofthe frame permanently changes shape or dimension in response to impactof the frame with another body, and more particularly to a body framefor an electric vehicle having structural members adapted to absorbenergy from frontal impacts which extend under a front portion of thebody frame, including structure for retarding motion by positiveengagement of elements, where relatively at least one member is adaptedto be deformed beyond its elastic limit to restrain relative motion.

BACKGROUND

During frontal impacts defined in Insurance Institute for Highway Safety(IIHS) and Federal Motor Vehicle Safety Standard (FMVSS) protocols,front structural members deform into the engine/motor compartment andbody cabin. In these areas, electric or hybrid electric vehicles willhave high voltage (HV) components (e.g. an inverter in the motorcompartment and a battery under the body cabin, DC-DC converter,charger). These parts may be positioned in a traditional crush zoneand/or a new crush zone presented by the removal of the much largerinternal combustion engine and supporting structures.

High voltage (HV) inverters are typically protected by a thick case toresist any crushing force or packaged outside of the expected crushzone. High voltage (HV) batteries are typically packaged outside oftraditional crush zones to avoid deformation of battery arrays. Removalof traditional load paths result in increased body cabin deformationunless appropriate alternative structures are added.

The large mass for an inverter case is counter-productive for a longrange electric vehicle (EV). Thus a more mass effective option isneeded. Battery arrays packaged outside of a crush zone are typicallysmaller and thus limit drivable range for the vehicles. Overall, allhigh voltage (HV) components must be protected from damage during crashimpacts while maximizing drivable range through larger batteries and lowmass protection structures.

SUMMARY

A frame structure for a land vehicle has wheels to engage a surface overwhich the vehicle moves. An electric motor enables the vehicle to bemoved along the surface. The frame structure provides support for avehicle body. At least a portion of the frame structure permanentlychanges shape in response to impact of the frame structure with anotherbody. The frame structure is adapted to absorb energy from frontalimpacts. The frame structure extends under a front portion of the bodyframe. The frame structure includes a rear sub-frame located below andin front of a pair of side frame under-members. At least one ramp isconnected to a side frame under-member for directing rearward slidingmovement of the rear sub-frame and attached structures downwardlybeneath a battery assembly.

A method is disclosed of assembling structural members for absorbingenergy from frontal impacts, where the frame structure permanentlychanges shape in response to impact of the frame structure with anotherbody. The frame structure extends under a front portion of the bodyframe. The method includes locating a rear sub-frame below and in frontof a pair of side frame under-members, and connecting at least one rampto a side frame under-member for directing rearward sliding movement ofthe rear sub-frame and attached structures rearward downwardly beneath abattery assembly.

A frame structure is adapted to absorb energy from frontal impacts. Theframe structure extends under a front portion of the body frame. Theframe structure includes a rear sub-frame located below and in front ofa pair of side frame under-members, and at least one ramp connected tothe pair of side frame under-members for directing rearward slidingmovement of the rear sub-frame and attached structures downwardlybeneath a battery assembly.

Other applications of the present invention will become apparent tothose skilled in the art when the following description of the best modecontemplated for practicing the invention is read in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The description herein makes reference to the accompanying drawingswherein like reference numerals refer to like parts throughout theseveral views, and wherein:

FIG. 1 is a bottom view of a front end of a vehicle having front andrear sub-frames and a pair of side frame under-members, an inverterprotection brace extends between the front and rear sub-frames,reinforcement brackets are attached to the pair of side frameunder-members, ramps are connected to the reinforcement brackets, and atether is connected between the pair of side frame under-members and therear sub-frame;

FIG. 2 is a perspective view of a top of the rear sub-frame withattached structure, such as a steering gear, and depicts an A-point boltconnection location and a B-point bolt connection location;

FIG. 3 is perspective view of a bottom of the pair of side frameunder-members showing B-point bolt connection locations in phantom andreinforcement brackets attached to the pair of side frame under-members;

FIG. 4A is a perspective view of a passenger side reinforcement bracket;

FIG. 4B is a bottom view of the passenger side reinforcement bracket ofFIG. 4A;

FIG. 4C is a front view of the passenger side reinforcement bracket ofFIGS. 4A-4B;

FIG. 4D is a side view of the passenger side reinforcement bracket ofFIGS. 4A-4C;

FIG. 5A is a perspective view of a driver side reinforcement bracket;

FIG. 5B is a bottom view of the driver side reinforcement bracket ofFIG. 5A;

FIG. 5C is a front view of the driver side reinforcement bracket ofFIGS. 5A-5B;

FIG. 5D is a side view of the driver side reinforcement bracket of FIGS.5A-5C;

FIG. 6 is perspective view of a bottom of the pair of side frameunder-members showing ramps attached to the reinforcement brackets;

FIG. 7A is a perspective view of a passenger side ramp;

FIG. 7B is a bottom view of the passenger side ramp of FIG. 7A;

FIG. 7C is a front view of the passenger side ramp of FIGS. 7A-7B;

FIG. 7D is an inboard side view of the passenger side ramp of FIGS.7A-7C;

FIG. 7E is an outboard side view of the passenger side ramp of FIGS.7A-7D;

FIG. 8A is a perspective view of a driver side ramp;

FIG. 8B is a bottom view of the driver side ramp of FIG. 8A;

FIG. 8C is a front view of the driver side ramp of FIGS. 8A-8B;

FIG. 8D is an outboard side view of the driver side ramp of FIGS. 8A-8C;

FIG. 8E is an inboard side view of the driver side ramp of FIGS. 8A-8D;

FIG. 9A is a perspective view of a bottom of the front and rearsub-frames showing the inverter protection brace connecting the frontand rear sub-frames;

FIG. 9B is a perspective view of a top of the inverter protection braceof FIG. 9A showing a gusset on a front end and a bolted connection on arear end;

FIG. 10A is a perspective view of a top of the tether;

FIG. 10B is a bottom view of the tether of FIG. 10A;

FIG. 10C is a side view of the tether of FIGS. 10A-10B;

FIG. 11A is a simplified side view of front end of a motor vehicleillustrating an inverter, side frame under-member, inverter protectionbrace, reinforcement bracket, ramp, rear sub-frame, and steering gear attime zero prior to a frontal impact;

FIG. 11B is a simplified side view of front end of a motor vehicleillustrating an inverter, side frame under-member, inverter protectionbrace, reinforcement bracket, ramp, rear sub-frame, and steering gear at44 milliseconds (ms) time after a frontal impact, where the inverterprotection bracket hits a wall, the front sub-frame starts deformation,and a pocket starts to form;

FIG. 11C is a simplified side view of front end of a motor vehicleillustrating an inverter, side frame under-member, inverter protectionbrace, reinforcement bracket, ramp, rear sub-frame, and steering gear at68 milliseconds (ms) time after a frontal impact, where the rearsub-frame approaches the ramp, maximum front sub-frame crush occurs asthe inverter protection brace rotates under the attachment knuckle andloads wall directly, back side of pocket releases B-point connection ofrear sub-frame, tether loading begins, and ramp slide begins, whereloading through the inverter protection brace and rear sub-frameA-points allows front frame side member to deform between the A and Bpoints (not shown);

FIG. 11D is a simplified side view of front end of a motor vehicleillustrating an inverter, side frame under-member, inverter protectionbrace, reinforcement bracket, ramp, rear sub-frame, and steering gear at76 milliseconds (ms) time after a frontal impact, where tether releases,rear sub-frame is crushed to maximum amount, and ramp slide picks up,and the rear sub-frame detaches from the front frame side member at thetime of tether separation;

FIG. 11E is a simplified side view of front end of a motor vehicleillustrating an inverter, side frame under-member, inverter protectionbrace, reinforcement bracket, ramp, rear sub-frame, and steering gear at100 milliseconds (ms) time after a frontal impact, where loading ofsteering gear starts, ramp slide approaches maximum, additional loadthrough ramp initiates under-member weld separation, and inverter showsminimal damage;

FIG. 12 is a simplified graph showing an approximated IIHS ODB responseforce in kiloNewton (kN) versus stroke in millimeter (mm), where thedouble dashed line illustrates a strongly connected inverter protectionbrace to the front sub-frame (no rotation at knuckle resulting in earlycollapse of the front frame side member behind the A-point), a hard rampwith slide (i.e. easily separating B-point bolt connection), the solidline illustrates a strong yet deformable attachment for the inverterprotection brace (delays front frame side member collapse), areinforcement bracket forming an energy absorption pocket in the sideframe under-member in combination with a ramp and a steering gearcatcher, and the single dashed line illustrates a high massed initialvehicle with a strong yet deformable attachment for the inverterprotection brace, a reinforcement bracket forming an energy absorptionpocket in the side frame under-member in combination with a ramp, asteering gear catcher and a tether;

FIG. 13A is a detailed view of a side frame under-member, reinforcementbracket, and B-point attachment location, where movement of the rearsub-frame is shown in various time segments corresponding to FIGS.11A-11E (i.e. t=0 ms; t=44 ms; t=68 ms; t=76 ms; t=100 ms) during energyabsorption pocket formation;

FIG. 13B is a cross sectional view of the side frame under-member,reinforcement bracket, and B-point attachment taken as shown in FIG.13A;

FIG. 14A is a simplified schematic of a tether and rear sub-frame, wherea rotational arrow is shown for the tether in response to rearwardmovement of the rear sub-frame; and

FIG. 14B is a simplified schematic of a ramp, rear sub-frame and arotational arrow for the tether in response to rearward movement of therear sub-frame, where a combined rotational path defines a progressivelynarrowing gap between the rear sub-frame and ramp, such that D₀>D₁>D₂,increasing crushing contact and friction.

DETAILED DESCRIPTION

The purpose of the construction method and the vehicle frame structure10 is to protect the high voltage (HV) inverter 12 in the motorcompartment 14 and the HV battery array (battery) 16 under the bodycabin 18 from deformation and damage during a frontal impact event. Inaddition, the body deformation is controlled such that the body cabin 18maintains suitable clearance for occupants. The construction method andframe structure 10 will allow the high voltage (HV) inverter 12 to beprotected by a safety cage 20. The previously know safety cage wastypically large mass or approximately ten kilograms (kg), where are thesafety cage of the disclosed frame structure 10 may be only fivekilograms (kg). The inverter 12 can be placed in traditional frontalimpact crush zones with the disclosed construction method. The battery16 is able to be packaged in a traditional crush zone by deflecting thepath of intruding structures beneath the battery and by improving theenergy absorbing characteristics of the deforming system in this area.By controlling body cabin 18 deformation, by maintaining energyabsorption (EA), and by adding new load paths, the standard of safetyfor electric or hybrid-electric vehicles (Federal Motor Vehicle SafetyStandards (FMVSS) and Insurance Institute for Highway Safety (IIHS)tests) is maintained to a similar level as traditional internalcombustion (IC) engines.

Development of the frame structure system revolved around five concernsto be addressed. First, the high voltage (HV) inverter 12 is packaged ina traditional crush zone. To protect the high voltage inverter 12, asafety cage 20 needs to be established around the location of theinverter 12. An inverter protection brace 22 can be added to connect afront support structure (sub-frame) 24 to a rear sub-frame 26. The rearsub-frame 26 attaches at A-point bolt connections 56 a, 56 b and B-pointbolt connections 34 a, 34 b. The inverter protection brace load throughthe A-point bolt connection changes the deformation mode of the frontframe side members between the A-point bolt connection and the B-pointbolt connection. Loading from the inverter protection brace 22 travelsthrough the rear sub-frame 26 to the A-point bolt connections 56 a, 56 blocated on a pair of front frame side members 50 a, 50 b resulting inearlier front frame side member deformation. Protection space is securedwith the inverter protection brace 22, but as a result of the inverterprotection brace direct loading of the barrier wall and additionaldeformation of the front frame side members the rear sub-frame 26rearward displacement is increased. Second, the increase in rearsub-frame 26 rearward displacement results in intrusion into a supporttray for the battery 16. The trajectory of the rear sub-frame 26 can bechanged by adding body and/or sub-frame ramps 28 a, 28 b. The initialconcept succeeds in lowering a path of the rear sub-frame 26 below themodules of the battery 16, but effectively removes a load path throughthe battery support from the frontal impact structure resulting inincreased body cabin 18 deformation. Third, deflection of the rearsub-frame 26 below the battery 16 removes that load path (and inconjunction with removal of the traditional internal combustion (IC)engine) results in additional body cabin 18 deformation from the loss ofthat EA member. A reinforcement bracket 30 a, 30 b can be added to theside frame under-member 32 a, 32 b behind a B-point connection 34 a, 34b with enough clearance to facilitate formation of a pocket 36 a, 36 bto form during rear sub-frame 26 rearward motion. In conjunction withthe front frame side member deformation between the A and B pointconnection the rear sub-frame 26 deforms at the A-point bolt connections56 a, 56 b and at least one of the pair of side frame under-members 32a, 32 b buckles rearward of the B-point bolt connections 34 a, 34 b forenergy absorption during frontal impacts. A pocket 36 a, 36 b is formed,reinforced by added bracket, in the side frame under-member 32 a, 32 bcreating good energy absorption (EA) and the resulting temporary lockupwith reinforcement bracket 30 a, 30 b deforms the side frameunder-member 32 a, 32 b rearward. Eventually, the pocket 36 a, 36 bbreaks, releasing the B-point attachment, and sliding movement of therear sub-frame 26 relative to the side frame under-member 32 a, 32 bbegins. Further improvement can be provided at the point where energyabsorption (EA) drops corresponding to the beginning of rearward slidingmovement of the rear sub-frame 26. Fourth, when the rear side of thepocket 36 a, 36 b breaks a force drop occurs corresponding to free rearsub-frame 26 slide. In order to limit the drop in EA from free sub-frameslide a catch and engage system can be provided. A front edge orcatching surface 38 of the ramp 28 a can be aligned with a steering gear40 and B-point bolt connection 34 a. The front edge 38 of the ramp 28 acan be changed to act as a stopper or catcher for the steering gear 40.The steering gear 40 loads the ramp 28 a directly and then the sideframe under-member 32 a welds begin to separate rearward to mitigateforce levels. The locked together rear sub-frame and catching featuremove rearward in tandem with under-member weld separation. This improvesthe energy absorption (EA) condition until the rear sub-frame 26slips-off. Fifth, it would be desirable to prevent early rear sub-frame26 slip-off of ramp 28 a, 28 b and side frame under-member 32 a, 32 b. Atether 44 can be added by modification of a noise-vibration (NV) andride & handling brace to support the rear sub-frame 26 upward intoenergy absorption (EA) structures during a rearward stroke. The rearsub-frame 26 slip can be delayed until almost all energy from a frontalimpact is absorbed. The rear sub-frame 26 locus is still beneath battery16. The frame structure can be generally defined in the field as eithera uni-body construction where the frame members provide support for abody cabin welded to the frame, a body-on-frame design where the cabinis fastened to the frame structure, or other variants (such as monocochestructures).

The frame structure system has five components which can be usedindividually or in any combination. First, an inverter protection brace22 can be connected to the front sub-frame 24 and a rear sub-frame 26,which protects inverter 12 by establishing a strong safety cage 20.Second, the addition of body ramps 28 a, 28 b deflect the rear sub-frame26 path beneath the battery 16, but increases the rear sub-frame 26motion (from increased mass, and/or removal of the traditional internalcombustion (IC) engine load path, and/or increased input load from motormount or brace structure) because no load is applied to a frame of thebattery 16 and the effect of ramping reduces the natural tendency forrear sub-frame to body interference. Third, reinforcement brackets 30 a,30 b can be added on the vehicle side frame under-members 32 a, 32 bpositioned rearward of the rear sub-frame 26 attachment point. The rearsub-frame 26 is driven rearward against the side frame under-member 32a, 32 b deforming the side frame under-member 32 a, 32 b and creating apocket 36 a, 36 b of shape which is defined by the position of thereinforcement bracket which absorbs energy and slows the vehicle. Afterthe rear sub-frame 26 fully deforms the pocket 36 a, 36 b, the pocket 36a, 36 b tears and the rear sub-frame 26 is released. Fourth, a contactsurface 38 can be added on the ramps 28 a, 28 b to allow catching of thesteering gear 40, which is mounted on the top surface of the rearsub-frame 26. The catching of the steering gear 40 in conjunction withthe pocket 36 a, 36 b allows more energy absorption to occur as the sideframe under-member 32 a, 32 b welding begins to separate from thevehicle as the locked structure moves rearward. The rear sub-frame 26slips at a later timing than without this catching surface 38. Fifth,body noise-vibration (NV) and ride-and-handling braces can be modifiedto act as a sub-frame tether 44. This tether 44 is able to control therear sub-frame 26 motion such that additional crush is required toadvance the rear sub-frame 26 rearward. The tether 44 separates aftermost of the energy is removed from the system. In some cases it may bebeneficial to keep the tether 44 attached to prevent release of freeparts from the vehicle during a crash.

Referring now to FIGS. 1, 9A-9B and 11A-11E, the inverter protectionbrace 22 connects the front sub-frame 24 to the rear sub-frame 26 bybolt-on connections at a front end and a rear end. The motor, which isattached to the rear sub-frame 26, rotates out of the path of theintruding side member taking the inverter 12 with the motor. Theinverter protection brace 22 has a gusset 46 at the front end connectedto the front sub-frame 24 to load a beam section without overloadingattachment bolts. The gusset 46 is connected to the front sub-frame at alocation outboard from a centerline of the vehicle. A portion of theinverter protection brace 22 load through the A-point bolt connectioncontributes to deformation timing and shape of the front frame sidemembers between the A-point bolt connection and the B-point boltconnection. The gusset 46 rotates below the front sub-frame 24 to delayloading of the inverter protection brace 22 and delay bending of thefront frame side members 50 a, 50 b to improve energy absorption of thefront frame side members 50 a, 50 b during frontal impacts. On the rearend, the inverter protection brace 22 is attached by four bolts to therear sub-frame 26 with an effective hinge portion 48 forward of the rearbolt connections. The bolted connection is connected to the rearsub-frame 26 at a location outboard of the centerline of the vehicle andinboard of the gusset 46 location. The gusset 46 connection is able todeform under the front sub-frame to delay loading of the inverterprotection brace. Loading from the inverter protection brace 22 travelsthrough the rear sub-frame 26 to the A-point bolt connections 56 a, 56 blocated on a pair of front frame side members 50 a, 50 b. The timing ofthis load, dictated by the inverter protection brace front attachmentkinematics, affect the front frame side member bending between the A andB point connections. The rear sub-frame 26 deforms at the A-point boltconnections 56 a, 56 b. The inverter protection brace 22 deformsadjacent the bolted connection at the rear end to form a safety cagearound an inverter during frontal impacts. The inverter protection brace22 effectively creates a safety cage 20 around the inverter 12, as bestseen in FIGS. 11A-11E during a frontal impact. Two configurations werestudied for the inverter protection brace 22: a strong dual pipestructure; and a stamped structure with internal brace. The frontattachment of the inverter protection brace 22 to the front sub-frame 24is gusseted to provide a strong connection through a knuckle or a gussetthat allows for translational motion under the front sub-frame 24 todelay front frame side member collapse behind the A-point. The inverterprotection brace 22 has an elongate angled shape angling inboard withrespect to a centerline of the vehicle adjacent a rear end. The inverterprotection brace 22 has a generally concave arcuate shape from front torear. This inverter protection brace 22 is able to transferapproximately two hundred kilo-Newton (kN) of force rearward until therear sub-frame 26 attachment to front frame members 50 a, 50 b fails andthe rear sub-frame 26 is released from the side frame under-members 32a, 32 b.

Replacement of the internal combustion engine with a much smallerelectric motor removes the traditional load path through the firewallfor frontal impact. Removal of this load path results in additionalfront frame side member deformation and rear sub-frame 26 motion whichis directed toward the modules of the battery 16 in long range electricvehicles. These batteries 16 must be protected against rear sub-frame 26attack. The addition of ramping structures 28 a, 28 b to the vehicleside frame under-member 32 a, 32 b and/or rear sub-frame 26 preventsthis damage by directing intruding structures beneath the batteries 16.The ramp structure 28 a, 28 b increases safe packaging volume allowingthe inclusion of a higher volume of cells for the battery 16 in thevehicle. The higher volume of battery cells increases the range of anelectric vehicle. The ramping structure 28 a, 28 b allows a margin ofsafety for even higher crash energies not included in governmenttesting. The motor/transmission is attached to the rear sub-frame 26 ofthe vehicle. The rear sub-frame 26 is able to move rearward into thevehicle side frame under-members 32 a, 32 b and begin ramping downbolt-on ramp structures 28 a, 28 b. These ramps 28 a, 28 b have multipleinterface angles to allow sliding of the rear sub-frame 26 and attachedstructures (steering gear 40, motor mount, bolts) down the angle andbeneath the battery 16 for multiple frontal crash directions. A ramp 28a, 28 b on the body is welded or bolted to the vehicle side frameunder-member 32 a, 32 b. The ramp 28 a, 28 b is aligned with a chamferedsurface 26 a of the rear sub-frame 26 to allow sliding. The pitch angleof the ramp 28 a, 28 b is set such that crushing of the ramp 28 a, 28 band rear sub-frame 26 is accounted for in the ramping trajectory, suchthat attached structures of the rear sub-frame pass below the batterystructure. A bolt-on type ramp 28 a, 28 b is illustrated in FIGS. 1, 6,7A-7E, 8A-8E, and 11A-11E which allows ramping on the interface shape.During some modes the ramp 28 a, 28 b is designed to act as a catchingdevice 38 for the rear sub-frame 26 and attached structures to improveenergy absorption (EA) response of the vehicle system.

Referring now to FIGS. 1, 3, 4A-4D, 5A-5D, 11A-11E and 13A-13B, removalof the internal combustion (IC) engine load path through the firewallresults in more rear sub-frame 26 intrusion. In addition, batterymodules 16 require protection from the intruding rear sub-frame 26.Using a deflection technique for the rear sub-frame 26 results in a lossof energy absorption (EA) as the rear sub-frame 26 structure slideseasily beneath the battery 16. This loss of energy absorption (EA) atthe rear sub-frame 26 results in more side member deformation andincreased load to the rocker. Both of which contribute to more intrusionto the body cabin 18 safety cage. Strong non-deformable ramps 28 a, 28 ballow easy separation of B-point bolt connections 34 a, 34 b andsliding. Low energy absorption (EA) is realized, but good trajectory isaccomplished. Locating ramps 28 a, 28 b too close to the rear sub-frame26 results in quick separation of the rear sub-frame and an early lossof energy absorption (EA). Thus a space is created using a reinforcementbracket 30 a, 30 b positioned such that buckling of a bottom wall 52 aof the side frame under-member 32 a, 32 b occurs between the B-pointbolt connection and a front edge 30 i, 30 j of the reinforcement bracket30 a, 30 b, while a boundary strength of a rearward wall of adeformation pocket 36 a, 36 b is defined by an outboard reinforcing edge30 k, 301 of the bracket 30 a, 30 b. The pocket 36 a, 36 b is able totemporarily restrain the rear sub-frame 26 restoring a load path beforeslippage and energy absorption (EA) loss.

A reinforcement bracket 30 a, 30 b can serve a multi-purpose: i.e.attachment point for battery 16, attachment point for ramps 28 a, 28 band acting as an energy absorption (EA) pocket 36 a, 36 b facilitator.Attaching the battery 16 and ramp 28 a, 28 b to the reinforcementbracket 30 a, 30 b prevents relative movement between the two parts andprovides a higher margin of safety. The reinforcement bracket 30 a, 30 bcan be added to the vehicle side frame under-member 32 a, 32 b. Thereinforcement bracket 30 a, 30 b can be welded to the pair of side frameunder-members 32 a, 32 b at a location rearward and inboard of a B-pointattachment 34 a, 34 b of the rear sub-frame 26 to the pair of side frameunder-members 32 a, 32 b. The rear sub-frame 26 can have a section whichoverlaps with the side frame under-member 32 a, 32 b at the B-point boltconnection 34 a, 34 b as best seen in FIGS. 13A-13B. During impact, theB-point bolt connection 34 a, 34 b is loaded as the rear sub-frame 26moves rearward (as illustrated in phantom lines for t=44, t=68, andt=78). The location of the reinforcement bracket 30 a, 30 b is such thatbuckling of the bottom wall 52 a of the side frame under-member 32 a, 32b starts to occur and a pocket 36 a, 36 b is formed providing goodenergy absorption (EA) as the side frame under-member 32 a, 32 b isdeformed and rear sub-frame 26 moves rearward. The reinforcement bracket30 a, 30 b facilitates formation and controls a deformation shape of anenergy absorption pocket 36 a, 36 b in the side frame under-member 32 a,32 b forward of and outboard of the reinforcement bracket 30 a, 30 bduring a frontal impact for temporarily restraining the rear sub-frame26 prior to the rear sub-frame 26 being released from a B-point boltconnection 34 a, 34 b to the side frame under-member 32 a, 32 b andallowed to slide past the reinforcement bracket 30 a, 30 b. After thepocket 36 a, 36 b fully deforms, then the pocket back wall (shape andposition defined by the location of the bracket) 52 b tears releasingthe rear sub-frame 26 to slide past the reinforcement bracket 30 a, 30b. As best seen in FIG. 13A, a position of the rearward wall 52 bdetermines an initiation strength of the bottom wall 52 a buckling forpocket 36 a, 36 b formation. An angular position of the reinforcementoutboard back wall 52 b of the side frame under-member 32 a, 32 bdetermines a strength of the back wall 52 b and deformed shape of theenergy absorption pocket 36 a, 36 b.

In this embodiment the battery 16 and ramps 28 a, 28 b both attach tothis reinforcement bracket 30 a, 30 b. The reinforcement bracket 30 a,30 b defines an attachment for a battery 16 located rearward of thereinforcement bracket 30 a, 30 b, and an attachment for a ramp 28 a, 28b connected to a bottom wall 30 c, 30 d of the reinforcement bracket 30a, 30 b for directing rearward movement of the rear sub-frame 26 beneaththe battery 16. This construction prevents relative motion between thetwo structures increasing robustness. The reinforcement bracket 30 a, 30b includes a bottom wall 30 c, 30 d and a pair of upwardly extendingsidewalls 30 e, 30 f, 30 g, 30 h on opposite sides of the bottom wall 30c, 30 d, at least one sidewall 30 e, 30 g bending in an outboarddirection at a forward end.

The reinforcement bracket 30 a, 30 b can be attached to the vehicle sideframe under-member 32 a, 32 b by way of body welding. Both the ramps 28a, 28 b and the battery 16 can be attached in such a way that relativemotion between the two structures is not allowed. The reinforcementbracket 30 a, 30 b is positioned rearward on the side frame under-member32 a, 32 b connection to the rear sub-frame 26, such that the rearsub-frame 26 can move rearward before creating the pocket 36 a, 36 b.

Referring now to FIGS. 1-2, 6, 8A-8E, and 11A-11E, to reestablish a loadpath between the rear sub-frame 26 and the side frame under-members 32a, 32 b after separation of the rear sub-frame 26 from the vehicle sideframe under-members 32 a, 32 b occurs, a steering gear 40 mounted to topside of the rear sub-frame 26 as best seen in FIG. 2 is used as a loadpath to push against an underbody structure, such as ramp 28 a and/orcatcher surface 38. The elimination of the internal combustion engineremoved the traditional load path between the frontal impact barrierthrough the engine into the fire wall. This results in more side memberdeformation and more rear sub-frame 26 rearward stroke. In order toprevent battery 16 damage in long range electric vehicles (EV) and toprevent body cabin 18 deformation new load paths were explored. A framestructure system includes a deflection method to send the rear sub-frame26 beneath the battery 16 that results in a substantial load drop oncedeflection of the rear sub-frame 26 by the ramps 28 a, 28 b occurs asoverall interference between the rear sub-frame and vehicle frame isreduced. This load drop results in increased body cabin 18 deformationas the remaining energy must be absorbed by the remaining structure.

A catching structure 38 can be added to promote additional energyabsorption through locking of the catching structure 38 with respect tothe rear sub-frame 26, such that continued rearward motion of the lockedcatching structure 38 and rear sub-frame 26 results in weld separationand crush of the side frame under-members 32 a, 32 b. By adding acatcher surface 38 on the deflection ramp 28 a, 28 b, the rear sub-frame26 is slowed and energy absorption occurs as the locked rear sub-frameand catching surface requires additional crush and weld separation ofthe side frame under-member as the temporarily locked structures moverearward helping to mitigate the effects of the deflection on the bodycabin 18. The deflection ramp 28 a, 28 b can be modified to include astanding flange or catching surface 38 that is able to engage thesteering gear 40 mounted on a top side of the rear sub-frame 26, as bestseen in FIG. 2, and catch protruding features from this steering gear 40housing. The flange or catching surface 38 on the ramp 28 a, 28 b ispositioned in both the width and height position to provide good overlapwith the intrusion locus of the rear sub-frame 26 for frontal impactmodes (offset deformable barrier (ODB), frontal rigid barrier (FRB),left angle rigid barrier (LARB)). As the rear sub-frame 26 separatesfrom the side frame under-member 32 a, 32 b, the rear sub-frame 26 movesrearward either crushing or sliding along the other under bodycomponents. As more sliding occurs, the reaction force drops and morebody cabin 18 intrusion results. By catching the rear sub-frame 26 byinteracting with the steering gear 40, motor mount, or additionalstructures the reaction load can be kept relatively high improvingloading efficiency and limiting load transfer through the side memberand toe-pan. An edge surface 28 of the ramp 28 a, 28 b is modified tocapture the steering gear 40 as the rear sub-frame 26 moves backwardtoward the battery 16.

Referring now to FIGS. 1, 10A-10B, 11A-11E and 14A-14B, to maximizeunderbody energy absorption, a tether 44 is used to hold the rearsub-frame 26 against the ramp 28 a, 28 b to improve crushing trajectoryinstead of allowing easy slide and loss of the load path. In additionthis method increases the resulting normal force and resulting friction.The loss of energy absorption arises as a result of adding body sideramps 28 a, 28 b. A very strong tether 44 could conceptually controlrear sub-frame 26 motion from initial impact and force additional Xdirection energy absorption (EA) instead of allowing slip-off. Without atether 44, reliance is placed on rear sub-frame 26 interaction with theunderbody to keep contact. With a tether 44, more freedom for load angleis achieved which will allow better motion control. The tether 44 aidsto keep all moving parts in contact while prescribing additionalcrushing deformation and increasing friction. The steel tether 44modifies an existing noise-vibration (NV) and ride and handling brace toimprove the loading direction of the rear sub-frame 26 against theunderbody. The tether 44 is attached to the vehicle side frameunder-member 32 a, 32 b at two outboard locations 54 a, 54 b using abolt and reinforced bearing surface. The tether 44 is then attached tothe rear sub-frame 26 at two B-point inboard locations 34 a, 34 b.

During frontal impact, the deformation of the rear sub-frame 26 rearwardbreaks the B-point bolt connection 34 a, 34 b from the side frameunder-member 32 a, 32 b. As the rear sub-frame 26 starts to slide downthe ramp 28 a, 28 b, the tether 44 holds the rear sub-frame 26 uprequiring additional crushing of both the side frame under-member 32 a,32 b and rear sub-frame 26 resulting in greater energy absorption. Thetether 44 is able to provide an upward force against the rear sub-frame26 as the rear sub-frame 26 begins to slide down the ramp 28 a, 28 b.This allows other energy absorption (EA) structures to perform moreeffectively. The tether 44 attaches at a rear portion of the rearsub-frame 26 and at outboard locations 54 a, 54 b of a second pair ofside frame under-members 32 a, 32 b.

As best seen in FIGS. 14A-14B, the tether 44 is able to rotate, i.e.arrows 90 a, at the locations 54 a, 54 b of attachment to the side frameunder-member 32 a, 32 b. The tether 44 is angled forward from theout-board attachments 54 a, 54 b such that rearward motion of the rearsub-frame 26 slackens the tether 44 to a point where the tether 44 hasrotated to a position perpendicular to the vehicle axis. As the tether44 rotates, there is a limited degree of displacement, i.e. some Z-axisdisplacement, i.e. arrow 90 b, that is allowed for the rear sub-frame26. However, this Z-axis displacement is less than that demanded by thepitch set for the ramps 28 a, 28 b requiring additional crush of therear sub-frame 26 and a resulting higher friction, as best seen in FIG.14B. In other words, the tether 44 slack from rotation is less than theincrease in vertical displacement of the rear sub-frame 26 therebyrequiring additional crush of the rear sub-frame 26 and contactingcomponents before tether 44 separation. A combined trajectory path 92 ofthe rear sub-frame 26 along the ramps 28 a, 28 b restrained by thetether 44 extends through a progressively narrowing gap with decreasingclearance distances, where the clearance distances D₀>D₁>D₂. Theprogressively narrowing clearance gap requires additional crushing ofthe rear sub-frame 26 and resulting higher friction prior to separationof tether 44.

Referring now to FIGS. 11A-11E, these simplified images are for IIHS, 35mph, 40% offset-deformable-barrier, test mode. Referring now to FIG.11A, a simplified side view of a front end of a motor vehicleillustrates an inverter 12, side frame under-member 32 a, 32 b, inverterprotection brace 22, reinforcement bracket 30 a, 30 b, ramp 28 a, 28 b,rear sub-frame 26, front sub-frame 24, and steering gear 40 at time zeroprior to a frontal impact with a barrier wall W. In FIG. 11B, theinverter 12, side frame under-member 32 a, 32 b, inverter protectionbrace 22, reinforcement bracket 30 a, 30 b, ramp 28 a, 28 b, rearsub-frame 26, and steering gear 40 are depicted at 44 milliseconds (ms)of time after a frontal impact. The inverter protection brace 22 hits awall, the front sub-frame 24 starts deformation as the front attachmentgusset 46 rotates under the front sub-frame 24, and an energy absorptionpocket 36 a, 36 b starts to form as the rear sub-frame 26 is pushedrearward by the inverter protection brace 22 and initial bending of thefront frame side-members 50 a, 50 b between the A and B point attachmentlocations. FIG. 11C illustrates the inverter 12, side frame under-member32 a, 32 b, inverter protection brace 22, reinforcement bracket 30 a, 30b, ramp 28 a, 28 b, rear sub-frame 26, and steering gear 40 at 68milliseconds (ms) of time after a frontal impact. The rear sub-frame 26approaches the ramp 28 a, 28 b, maximum front sub-frame 24 crush occursas the inverter protection brace 22 loads the wall directly, the frontframe side member 50 a, 50 b bends rearward of the A-point, a back sideof pocket 36 a, 36 b releases B-point connections 34 a, 34 b of rearsub-frame 26, tether 44 loading begins, and rear sub-frame 26 slidealong ramps 28 a, 28 b begins. In FIG. 11D, the inverter 12, side frameunder-member 32 a, 32 b, inverter protection brace 22, reinforcementbracket 30 a, 30 b, ramp 28 a, 28 b, rear sub-frame 26, and steeringgear 40 are depicted at 76 milliseconds (ms) of time after a frontalimpact. The tether 44 releases, rear sub-frame 26 is crushed to amaximum amount, and rear sub-frame 26 slide along ramps 28 a, 28 b picksup as additional front frame side member 50 a, 50 b deformation occurs.FIG. 11E illustrates the inverter 12, side frame under-member 32 a, 32b, inverter protection brace 22, reinforcement bracket 30 a, 30 b, ramp28 a, 28 b, rear sub-frame 26, and steering gear 40 at 100 milliseconds(ms) of time after a frontal impact. Loading of the steering gear 40starts, rear sub-frame slide along ramps 28 a, 28 b approaches maximum,additional load through ramp 28 a, 28 b initiates side frameunder-member 32 a, 32 b weld separation in area 60, and the inverter 12shows minimal damage.

In the force versus stroke curves of FIG. 12, the double dashed line 100shows the combination of a semi-strong front attachment inverterprotection brace 22 and a ramp 28 a, 28 b welded directly to a frameunder-member providing a condition where ramping occurs early witheasily separating B-point bolt connection 34 a, 34 b of the rearsub-frame 26 from the side frame under-member 32 a, 32 b. Load from theinverter protection brace is transferred through the A-point bolt andcauses early front frame side member collapse and EA loss shown by thelower bound of the cross hatching 110. A large drop in energy absorption(EA) occurs shown by the lower boundary of dashed horizontal line 108due to easy slide. The solid line 102 illustrates the combination of andeformable front attachment inverter protection brace 22, a bolted ramp28 a, 28 b, a reinforcement bracket 30 a, 30 b providing a case withformation of an energy absorption pocket 36 a, 36 b in the side frameunder-member 32 a, 32 b providing a large additional energy absorption(EA) area shown in cross hatching 106 below the dashed horizontal line108. The side frame under-member 32 a, 32 b deforms to create an energyabsorption pocket 36 a, 36 b and subsequent tearing of the rearsub-frame 26 from the side frame under-member 32 a, 32 b. The crosshatching 110 shows the improvement in early EA from delaying loadingthrough the inverter protection brace by having a deformable frontattachment allowing rotation of the brace under the front sub-frame. Thesingle dashed line 104 shows a high vehicle mass result with thecombination of an deformable front attachment inverter protection brace22, a reinforcement bracket 30 a, 30 b forming an energy absorptionpocket 36 a, 36 b in the side frame under-member 32 a, 32 b, a ramp 28a, 28 b, a steering gear catcher 38, and a tether 44. The cross hatching110 shows the improvement in early EA from delaying loading (andtherefore delayed front frame side member collapse) through the inverterprotection brace by having a deformable front attachment allowingrotation of the brace under the front sub-frame. The cross hatched area106 corresponds to the additional energy absorption from initiation ofthe energy absorption pocket 36 a, 36 b in the side frame under-member32 a, 32 b by the reinforcement bracket 30 a, 30 b. The stippled area112 corresponds to the additional energy absorption attributable to thecatching surface 38 interacting with the steering gear 40 whilesupported in prolonged crushing contact with the ramps 28 a, 28 b bytether 44.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiments but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims, which scope is to be accorded the broadestinterpretation so as to encompass all such modifications and equivalentstructures as is permitted under the law.

What is claimed is:
 1. A frame structure for a land vehicle havingwheels to engage a surface over which the vehicle moves, an electricmotor enabling the vehicle to be moved along the surface, the framestructure providing support for a vehicle body, where at least a portionof the frame structure permanently changes shape in response to impactof the frame structure with another body, the frame structure adapted toabsorb energy from frontal impacts, the frame structure extending undera front portion of the vehicle body, the improvement of the framestructure comprising: a rear sub-frame located below and in front of apair of side frame under-members; and at least one ramp connected to thepair of side frame under-members for directing rearward sliding movementof the rear sub-frame and attached structures downwardly beneath abattery assembly.
 2. The improvement of claim 1, wherein the at leastone ramp has multiple interface angles and is aligned with a chamferedsurface of the rear sub-frame to allow sliding movement, while a pitchangle of each ramp is set to provide a trajectory of the rear sub-framemotion taking into account crushing of the ramp and the rear sub-framesuch that attached structures of the rear sub-frame pass below thebattery structure.
 3. The improvement of claim 2, wherein the ramps arebolted to the pair of side frame under-members.
 4. The improvement ofclaim 1 further comprising: a catching structure promoting additionalenergy absorption through locking of the catching structure with respectto the rear sub-frame, such that continued rearward motion results inweld separation and crush of the side frame under-members.
 5. Theimprovement of claim 1 further comprising: a catching surface formed onthe at least one ramp for engaging the rear sub-frame and attachedstructures to improve energy absorption during frontal impacts.
 6. Theimprovement of claim 5, wherein the catching surface interacts with asteering gear to promote additional crushing and energy absorptionduring sliding movement of the rear sub-frame relative to the at leastone ramp.
 7. The improvement of claim 1 further comprising: areinforcement bracket attached to the pair of side frame under-membersfor facilitating formation and controlling a deformation shape of anenergy absorption pocket in the corresponding side frame under-memberduring a frontal impact for temporarily restraining the rear sub-frameproviding an energy absorption path before the rear sub-frame isreleased and allowed to slide past the reinforcement bracket.
 8. Theimprovement of claim 7, wherein the reinforcement bracket providesattachment for the battery, attachment for the ramps, and facilitatesformation of the energy absorption pocket during frontal impacts.
 9. Theimprovement of claim 7, wherein the reinforcement bracket is welded tothe pair of side frame under-members at a location rearward and inboardof a B-point attachment of the rear sub-frame to the pair of side frameunder-members.
 10. The improvement of claim 7, wherein the reinforcementbracket facilitates buckling of a bottom wall of the pair of side frameunder-members and defines a boundary strength of a reinforcementoutboard rearward wall of the energy absorption pocket, wherein aposition of the rearward wall determines an initiation strength of thebottom wall buckling for pocket formation.
 11. The improvement of claim10, wherein an angular position of the reinforcement outboard rearwardwall of the side frame under-member determines a strength of a back walland a deformed shape of the energy absorption pocket.
 12. Theimprovement of claim 1 further comprising: a tether connected betweenthe pair of side frame under-members and the rear sub-frame for holdingthe rear sub-frame against the at least one ramp to increase energyabsorption.
 13. The improvement of claim 12 further comprising: anoise-vibration, ride and handling brace defining the tether, the tetherattaching to the pair of side frame under-members at two outboardlocations and to the rear sub-frame at two B-point inboard locationspositioned forward of the outboard locations.
 14. The improvement ofclaim 12, wherein the tether rotates at a location of attachment to thepair of side frame under-members providing a limited degree ofdisplacement away from the at least one ramp requiring additional crushof the rear sub-frame and higher friction.
 15. The improvement of claim12, wherein the tether is angled forward from the outboard attachments,such that during a frontal impact rearward motion of the rear sub-frameslackens the tether to a point where the tether rotates to a positionperpendicular to a vehicle axis.
 16. The improvements of claim 15,wherein the tether slack from rotation is less than an increase invertical displacement of the rear sub-frame thereby requiring additionalcrush of the rear sub-frame and attached structures before tetherseparation.
 17. A method of assembling structural members for absorbingenergy from frontal impacts of a frame structure for a land vehiclehaving wheels to engage a surface over which the vehicle moves, anelectric motor enabling the vehicle to be moved along the surface, theframe structure providing support for a vehicle body, where the framestructure permanently changes shape in response to impact of the framestructure with another body, the frame structure extending under a frontportion of the vehicle body, the method comprising: locating a rearsub-frame below and in front of a pair of side frame under-members; andconnecting at least one ramp to the pair of side frame under-members fordirecting rearward sliding movement of the rear sub-frame and attachedstructures rearward downwardly beneath a battery assembly.
 18. Themethod of claim 17 further comprising: providing a chamfered surface onthe rear sub-frame; providing multiple interface angles on the at leastone ramp; aligning the at least one ramp with the chamfered surface ofthe rear sub-frame to allow sliding movement; and providing a pitchangle on the at least one ramp set to provide a trajectory taking intoaccount crushing of the ramp and the rear sub-frame.
 19. The method ofclaim 17 further comprising: bolting the at least one ramp to the pairof side frame under-members.
 20. The method of claim 17 furthercomprising: forming a catching surface on the at least one ramp forengaging the rear sub-frame and attached structures to improve energyabsorption during frontal impacts.
 21. The method of claim 20 furthercomprising: promoting additional crushing by interacting the catchingsurface with a steering gear to increase energy absorption duringsliding movement of the rear sub-frame relative to the at least oneramp.
 22. The method of claim 17 further comprising: attaching areinforcement bracket to the pair of side frame under-members forfacilitating formation and controlling a deformation shape of an energyabsorption pocket in the corresponding side frame under-member during afrontal impact for temporarily restraining the rear sub-frame providingan energy absorption path before the rear sub-frame is released andallowed to slide past the reinforcement bracket.
 23. The method of claim22 further comprising: attaching the battery and the at least one rampthrough the reinforcement bracket to prevent relative motion between thetwo parts and provide a higher margin of safety.
 24. The method of claim22 further comprising: attaching the reinforcement bracket to the pairof side frame under-members at a location rearward and inboard of aB-point attachment of the rear sub-frame to the pair of side frameunder-members.
 25. A frame structure adapted to absorb energy fromfrontal impacts, the frame structure extending under a front portion ofa vehicle body, the frame structure comprising: a rear sub-frame locatedbelow and in front of a pair of side frame under-members; and at leastone ramp connected to the pair of side frame under-members for directingrearward sliding movement of the rear sub-frame and attached structuresdownwardly beneath a battery assembly.